Study on the bending behavior of CFRP-confined square concrete-filled steel tubes reinforced with internal latticed steel angles

The bending mechanical properties of FRP-confined square concrete-filled steel tubes (CFST) reinforced with internal latticed steel angles, including the failure modes, characteristic curves and characteristic mechanical parameters of tested specimens, were investigated through experiments in this paper. The bending mechanisms were also analyzed using an established finite element model, including the analysis of the bending moment borne by each component, the distributions of contact pressure between different components at the mid-span section, and the distributions of the neutral axis under the bending capacity. The key influential parameters, including the tensile strength and thickness of the FRP, were also examined. The results indicate that the FRP has almost no influence on bending stiffness, however, it enhances the yield bending moment and bending capacity to a certain extent. It was also found that the enhancement decreases as the width of steel tube increases, and the influence of FRP is more profound before reaching the peak load. The calculation formulas for the bending capacity were developed using the superposition method and numerical fitting method. Analysis of their accuracy shows that the formulation using the superposition method yields relatively accurate and safe prediction results, with the prediction errors of less than 20 %.